I've begun to really appreciate the power of economies of scale.
If you have one plant:
Lose one to dry weather, insects, fire, etc., and you've none left.
You don't have much to trade with.
If one tree doesn't produce in that year, you've got nothing.
You don't have much in one to eat...
If you have a few dozen:
If you lose a few, it's not a precarious situation.
You have plenty of produce to eat...
You have plenty to trade...
If you're producing something other than a foodstuff, it's easier to do things... Extracting essential oils - you generally need lots of leaves. A single tree won't be able to provide you much, but a dozen will give you lots. If you need to get the equipment to efficiently do a tree or two, it can easily be used for two dozen.
Of course, there's a lot to be said for variety, but if you have the possibility of trading with people, if you have plenty of a trade good, you won't be too badly off...
I've been looking for some good stainless steel stills for essential oils (and the like) - I can find copper ones easily, glass aplenty - but stainless steel seems to be harder to come by. I'd rather use that than copper, as I would expect the steel not to react as much... Of course, if it's a matter of what I can get... When you want some twenty litre or similar sized stills, you might have to put up with what you can get. Pre-SHTF, though, you have plenty of time to experiment, and make mistakes. Better to make mistakes before than after, I suppose.